A study found that women diagnosed with HER2-positive, metastatic breast cancer that grew while being treated with Herceptin (chemical name: tastuzumab) benefited from adding Tykerb (chemical name: lapatanib) to the Herceptin rather than switching from Herceptin to Tykerb. These results were presented at the 2009 San Antonio Breast Cancer Symposium.

HER2-positive cancers make too much of the HER2 protein. The HER2 protein sits on the surface of cancer cells and receives signals that encourage the cancer to grow and spread. About one out of every four breast cancers is HER2-positive. Both Herceptin and Tykerb are targeted therapy medicines that work by blocking the HER2 protein's ability to make HER2-positive breast cancers grow. Herceptin and Tykerb work in different ways. Herceptin blocks the protein on the cancer cell's surface. Tykerb blocks the protein inside the cell.

Herceptin is approved by the U.S. Food and Drug Administration (FDA) to treat advanced-stage, HER2-positive breast cancers and to lower the risk of cancer coming back (recurrence) in women diagnosed with HER2-positive, early-stage breast cancer with a high risk of recurrence.

Tykerb is approved by the FDA to be given in combination with Xeloda (chemical name: capecitabine), a type of chemotherapy, to treat HER2-positive, metastatic breast cancer that has stopped responding to anthracyclines, taxanes, and Herceptin.

Rather than stopping Herceptin and switching to Tykerb when metastatic breast cancer comes back or grows while being treated with Herceptin, many doctors have been adding Tykerb to the treatment plan and continuing Herceptin. The researchers who did this study wanted to know if that approach makes sense. The results suggest it does.

All 296 women in this study were diagnosed with HER2-positive, metastatic breast cancer. All the women were "heavily pretreated" before the study, which means each woman had received four or more courses of various chemotherapy medicines and the cancer had stopped responding to each one. Each woman's last treatment course before this study included Herceptin.

When the breast cancer grew while being treated with Herceptin, about half the women continued to get Herceptin and Tykerb was added to the treatment plan. The other women stopped getting Herceptin and switched to Tykerb.

During the study it became clear that adding Tykerb to Herceptin treatment was better than stopping Herceptin and switching to Tykerb. So more than half of the women (52%) who stopped taking Herceptin when they started on Tykerb "crossed over" and started Herceptin again.

No chemotherapy or hormonal therapy medicines were given to the women during this study.

Women treated with BOTH Tykerb and Herceptin lived an average of 14 months compared to 9.5 months for women who switched from Herceptin to Tykerb -- a 26% improvement in survival. Since many of the women who initially switched from Herceptin to Tykerb chose to cross over and get both Tykerb and Herceptin, it's possible that the survival benefits of the Herceptin-Tykerb combination may be even greater.

Herceptin is given intravenously and may cause side effects such as fever, chills, muscle aches, and nausea. These side effects usually are less severe after the first treatment. Herceptin also may cause heart damage that can be life-threatening in some cases. Herceptin costs about $10,000 per month.

Tykerb is a pill taken by mouth. Tykerb doesn't seem to cause the serious heart problems associated with Herceptin. The most common side effects of Tykerb are diarrhea, redness and tingling in the hands and feet, and a rash. These side effects usually aren't severe. Other side effects can include stomach upset, vomiting, and fatigue. Tykerb costs $5,000 to $6,000 per month.

The most common side effect seen in this study was diarrhea. One woman died from a heart problem, but the heart problem wasn't directly related to the Herceptin or Tykerb treatment.

If you're being treated with Herceptin for HER2-positive, metastatic breast cancer, you might want to talk to your doctor about the results of this study. Together you can decide if adding Tykerb to your treatment plan makes sense if the cancer stops responding to Herceptin alone.

Visit the Breastcancer.org Targeted Therapies section to learn more about Herceptin and Tykerb.